Table 6. Significance test of regression coefficient^a.

Variable	Coefficient	Std. Error	t-Value	p-Value
Intercept	2.002	0.0088	227.04	<0.0001b
X1	−0.0894	0.0070	−12.83	<0.0001b
X2	0.0211	0.0070	3.03	0.0191b
X1X2	−0.0125	0.0098	−1.27	0.2454
X1X1	−0.1329	0.0075	−17.77	<0.0001b
X2X2	−0.1579	0.0075	−21.12	<0.0001b

^aR² = 0.9918, R² (Adj) = 0.986. ^bStatistical signification at 95% of confidence level (p < 0.05).